i know that the Joomla update button was removed in the recent releases of Admin Tools.
But the "System - Admin Tools Joomla! Update Email" plugin is still available and on our site it is also enabled.
The php option allow_url_fopen is On and cURL support is enabled.
Also there is no firewall restriction for the joomla update url active, via "wget http://update.joomla.org/core/list.xml" i can downlaod the xml-file.
Could you give us a hint why we don't get update emails for new Joomla releases ?
(The Joomla update component is also telling that joomla is already up to date (Joomla 2.5.16) )
best wishes
Chin-Man